1. Field of the Invention
The field of the invention is adjustable orifice fluid dampers utilized in air and liquid handling systems such as those utilized in manufacturing and assembly clean rooms, ducts, pipes, air handling and fluid flow systems.
2. Description of the Related Art
Fluid flow systems rely on the accurate adjustment of the fluid medium in consideration of static and dynamic conditions. In many cases, dampers are utilized in fluid flow systems for accurate adjustment of the fluid medium.
Existing generic types of dampers in general use today which accomplish the goals of adjustment of fluid flow include multiple parallel blade type dampers wherein a number of elongated blades are placed in an arrangement such that the blades touch or overlap one another in the closed position to form a plane surface across the opening and to controllably restrict fluid flow. The blades rotate lengthwise about a shaft generally situated centrally of the blade.
In addition, multiple opposed blade dampers have a similar blade arrangement to the multiple parallel blade dampers wherein generally elongated blades are juxtaposed each other, rotating about a lengthwise centrally located shaft through the blade, the edges of the blades touching each other to effect a seal in the closed position or, when in the open position, are situated vanelike parallel to each other. The blades are linked together to move simultaneously, each blade, however, rotating in a direction opposite to that of the two adjacent blades.
Another system, namely, sliding single blade dampers, blocks all or a portion of the fluid passageway, the single blade slideable in and out of the passageway.
Another type of damper consists of a single blade, known as a butterfly, mounted on a shaft in the middle of the blade. As the shaft is rotated, the blade closes off the opening in its entirely or in part or reaches a point where the blade is parallel to the fluid stream, effectively opening the passageway to flow.
Lastly, and certainly not conclusively, are sliding orifice dampers generally consisting of two planar surfaces, each surface provided with a plurality of apertures for the passage of air or liquid. The movement of one plate relative to the other causes a variation in the effective area of the superimposed apertures, such that the effective area, or free area, available for fluid flow through the plates varies from zero (fully closed) to a maximum available defined by shape, size, and spacing of the apertures, when the two planar surfaces are in alignment. Current configurations of apertures in sliding plate dampers include circles, squares, rectangles, and elongated slots with and without circular ends. The pattern of the apertures usually takes on uniformly spaced columns and rows. The type of orifice and pattern of the apertures on each plate are identical, such that when the two plates are aligned, the resultant pattern is as if there were only one plate since the apertures of one plate match the apertures of the other plate.
The problem with the multiple parallel blade dampers, multiple opposed blade dampers, single sliding blade dampers, butterfly dampers, sliding orifice dampers, and all other damper systems known to the inventors, is that the relationship of fluid flow (from zero to maximum) versus damper position (from fully closed to fully open) is characteristically non-linear.
One widely used application of dampers to regulate fluid flow is in clean rooms wherein products are manufactured or assembled that require particle contamination be kept to a minimum. An example of this is clean room areas utilized in semiconductor manufacture. In clean rooms, airborne particulates are a significant source of contamination such that the product may well be rendered non-usable if contaminated. In clean room technology, filtered air enters the clean room via the ceiling from a plurality of equally spaced filtered openings (which may virtually encompass the whole ceiling) and may exit the clean room through the floor which is a series of grates or perforated panels. The air is then recirculated through the filters. It is important that the flow of air through the clean room be laminar from the ceiling to the floor so that contaminants in the air, or contaminants arising from the equipment in the room or from personnel in the room, fall straight to the floor and through the grille, or perforated panel and then captured in the filter system recirculating the air. Turbulence in the air, however, will cause the particulate matter to move horizontally or perhaps vertically upward and then downward thereby enhancing the possibility that airborne particles may contaminate the work product.
In many clean room applications, control of the air for laminar flow is attempted in part by an under-the-floor damper system which resides generally two or more inches below the floor grate or panel. Clean room damper systems are generally divided into cells, ranging in various rectangular and square configurations with sides of one to four feet. Many times the cell sizes are dictated by the mechanical constraints of the clean room, however, having a plurality of cells with contained damper systems does work to the advantage of clean room design. In clean rooms are typically situated work benches, work areas, and machinery. The work benches and machinery rest on the floor grate and as a consequence, it may not be possible for air to pass through the floor grate immediately underneath the pieces of equipment. Consequently, dampers in cells located under the floored equipment are usually closed to air passage.
In fact, clean room technology has advanced to the point where, when all the parameters are known, i.e., the size and placement of the standing equipment is known, air flow in the areas not covered by standing equipment can be calculated and determined for maintaining laminar flow of the air in the room. As earlier mentioned, air usually enters the clean room from the ceiling and substantially uniformly over the area of the ceiling. To maintain laminar flow or to reduce turbulence to a minimum, the flow through different areas of the floor will naturally be different.
The problem in the past has been that while the air flow through different areas of the floor to maintain laminar flow or minimum turbulence can be calculated, yet the damper technology heretofore is such that each damper in each cell passing air requires that the damper be experimentally adjusted to achieve the desired air flow. This results from the earlier stated characteristic of the existing damper technology in that the relationship between change in damper opening and fluid flow is non-linear. Consequently, the time that it takes to adjust clean rooms for laminar air flow can be quite prolonged.
Thus, it is readily apparent that it would be advantageous if the damper system utilized in fluid flow applications could be preset to calculated flow before or during constructing of the fluid handling system utilizing the damper systems.
Just as apparent, it would also be very advantageous if a damper system were available which exhibited characteristics of linearity between fluid flow and relative mechanical position of the elements which comprise the damper system.
More particularly, in a sliding orifice damper system, great advantage would accrue utilizing a damper system which provides a linear relationship between adjustment position (which can be repeatedly and accurately set) and fluid flow and thus afford the user the means to accurately predict system performance with a properly controlled fluid medium.